This application relates to optical spectral analysis including apparatus, systems and techniques for measuring optical spectrum of light.
Light can be used in a wide range of applications. One important property of light is the optical spectral property of the light, such as the frequency of the light, and the optical spectrum of light, i.e., the spectral composition of light in wavelength or frequency of the light. For example, behaviors of light signals can depend on the optical spectrum of a given light signal. For another example, the optical spectrum of a given light signal can be used to extract information of a device or material that interacts with the light signal.
Many techniques and devices can be used to analyze the optical spectrum of light. A device for measuring the optical spectrum of light is often referred to as an optical spectrum analyzer (OSA) and is designed to divide a light signal into its constituent wavelengths. The optical power of each constituent wavelength is measured and the measurements of the optical power levels can be graphically displayed with respect to the corresponding constituent wavelengths with the wavelength on the horizontal axis and the measured power on the vertical axis. The performance of an optical spectrum analyzer can be measured by various factors, including the spectral resolution, the spectral range, and the measurement speed.
Optical spectrum analyzers can be implemented various optical analysis mechanisms. Three commonly used mechanisms are 1) using a spatially dispersive element, such as a diffractive grating, to optically separate different spectral components of the light, 2) using a tunable narrow band filter, such as a F-P resonator or a tunable fiber Bragg grating, to sequentially select and detect one spectral component at a time and 3) using an optical interferometer (e.g., a Michaelson or Mach-Zehnder interferometer) to obtain optical interference measurements based on varying the path difference between two optical interfering arms and then performing Fast Fourier Transform (FFT) on the output of the interferometer.